Our interest in the phagocyte- and tumor cell-derived protein MFG-E8 continues but our level of effort has decreased. Currently, all of our effort in this area is via collaborative projects that are led or co-led by extramural investigators. In the past, we generated several MFG-E8 mouse mutants to determine if MFG-E8 has a role tumor biology and immunophysiology in vivo. Results, to date, indicate that tumor cells produce MFG-E8 and that MFG-E8 promotes tumorigenesis in both orthotopic and transgenic models of cancer in mice (melanoma, non-melanoma skin cancer, colon cancer and pancreatic beta-cell cancer). In addition, ongoing experiments suggest that MFG-E8 may be a relevant therapeutic target in cancer. To gain additional understanding of the roles that MFG-E8 plays in tumor formation and immunophysiology, we carefully localized MFG-E8 accumulation in vivo in tumors and in normal tissues. Utilizing highly specific affinity-purified polyclonal antibodies, we determined that MFG-E8 was found focally in vascular or perivascular locations and in other specific locations as well. We have documented that, in tumors, pericytes produce more MFG-E8, on a per cell basis, than leukocytes, endothelial cells and tumor cells. We hypothesized that pericyte-derived MFG-E8 regulates endothelial cell function and tested this hypothesis in several in vitro and in vivo models. We also hypothesized that pericyte-derived MFG-E8 might influence pericyte function, and we have demonstrated that MFG-E8 enhances perciyte migration in vitro. In the course of these studies, we determined that some of the anti-MFG-E8 antibodies that we have developed have function neutralizing activity in vitro. This led us assess the role of MFG-E8 in pathologic angiogenesis in the well characterized mouse oxygen-induced retinopathy model. In these studies, angiogenesis was attenuated in MFG-E8 knockout mice and in mice treated with some anti-MFG-E8 antibodies. Thus, MFG-E8 may represent a valid therapeutic target in diseases in which unwanted angiogenesis is a critical factor. We subsequently engaged in a series of in vitro experiments designed to provide insights into the mechanism(s) by which MFG-E8 enhances pericyte function and angiogenesis. Results of these experiments suggested that MFG-E8 potentiated PDGF signaling via a mechanism that is integrin-dependent and that may protect PDGF receptors from ubiquitin-dependent degradation. In collaboration with Dr. Sei-ichiro Motegi, a former post-doctoral fellow, we are studying the extent to which MFG-E8 regulates full-thickness wound healing. A recent publication demonstrates that MFG-E8 regulates angiogenesis in the setting of full thickness wound healing and that topical application of MFG-E8 promotes wound healing to some extent. We have initiated a collaboration with Dr. Nick Marsh-Armstrong of Johns Hopkins University to assess the possible involvement of MFG-E8 in normal physiology and pathophysiology in the central nervous system. In a separate collaboration with Dr. George Hajishengallis at U Penn, we are exploring MFG-E8 function in a unique inflammation model. In these now published experiments, Dr. Hajishengallis and coworkers determined that osteoclasts produce MFG-E8 and that MFG-E8 is a negative modulator of osteoclastogenesis. Bone loss was enhanced a model of peridontal inflammation and it was also increased in MFG-E8 knockout mice as compared with littermate contols. In perhaps related studies, Dr. Rauner has demonstrated that MFG-E8 may have an anti-inflammatory activity in rheumatoid arthritis in mice and humans. We are also collaborating with Dr. Harvey Florman at the University of Massachusetts to determine if MFG-E8 might have a role in female fertility.